Freenet. Freenet works, peer to peer. It doesn't care what the physical network is like. For a dial-up alternative, Fidonet. At some point, though, traditional server/client architecture is preferable.

<technical explanation>
Prime numbers are veryyy difficult to factor, but very easy to multiply to. And PGP essentially turns your password into a veryyyyy long prime number.
</technical explanation>

I'm not bright enough to be able to explain the way it works. But essentially, encryption exploits math to make a very difficult to undo password. As in, so difficult, you're more likely to colonize Jupiter and marry aliens before we'll be able to undo encryption.